[WIP] Update documentation to improve user discovery of -U option

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

#5762 brough up the question how one could have knwo about the -U option. Even though we mention the properties in the docs its true that actually forcing updates is not docuemnted anywhere. We should enahnce the docs at relevant locations to makes such things easier to discover for new users.

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[laeubi]

Lets see if this works better now with more context:

• Bug: 5762 Improve documentation for P2 transport cache and -U option #5817